Atrial natriuretic peptide (ANP), an endogenous hormone synthesized by the cardiac atria, has been shown to improve renal function in multiple animal models of acute renal failure. In a recent multicenter clinical trial of 504 patients with acute tubular necrosis (oliguric and nonoliguric), ANP decreased the need for dialysis only in the oliguric patients. In the present study, 222 patients with oliguric acute renal failure were enrolled into a multicenter, randomized, double-blind, placebo-controlled trial designed to assess prospectively the safety and efficacy of ANP compared with placebo. Subjects were randomized to treatment with a 24-hour infusion of ANP (anaritide, 0.2 microgram/kg/min; synthetic form of human ANP) or placebo. Dialysis and mortality status were followed up for 60 days. The primary efficacy end point was dialysis-free survival through day 21. Dialysis-free survival rates were 21% in the ANP group and 15% in the placebo group (P = 0.22). By day 14 of the study, 64% and 77% of the ANP and placebo groups had undergone dialysis, respectively (P = 0.054), and 9 additional patients (7 patients, ANP group; 2 patients, placebo group) needed dialysis but did not receive it. Although a trend was present, there was no statistically significant beneficial effect of ANP in dialysis-free survival or reduction in dialysis in these subjects with oliguric acute renal failure. Mortality rates through day 60 were 60% versus 56% in the ANP and placebo groups, respectively (P = 0.541). One hundred two of 108 (95%) versus 63 of 114 (55%) patients in the ANP and placebo groups had systolic blood pressures less than 90 mm Hg during the study-drug infusion (P < 0.001). The maximal absolute decrease in systolic blood pressure was significantly greater in the anaritide group than placebo group (33.6 versus 23.9 mm Hg; P < 0.001). This well-characterized population with oliguric acute renal failure had an overall high morbidity and mortality.